How do I create n canvases from within Javascript?
Question
I am looking for a way to create canvases as I need them at run time. my code so far is
var isCanv = new Array();//bool array for which places in the arrays are/are not in use
var canv = new Array();//for the canvases
var ctx = new Array();//for the contexts
var inhtml = new Array();//for the html canvas tags for each canvas
var upperBound = -1;//the highest index used so far
function createCtx(){
var i = 0;
while(isCanv[i]){
i++;
}
inhtml[i] = '<canvas id="canv'+i+'" width="'+800+'px" height="'+800+'px" style="display:block;background:#ffffff+;"></canvas>';
isCanv[i] = true;
if(i>upperBound){
upperBound = i;
}
var tohtml = '';
for(var j = 0; j<= upperBound; j++){
if(isCanv[i]){
tohtml+=inhtml[j];
}
}
document.getElementById('game').innerHTML=tohtml;
canv[i] = document.getElementById('canv'+i);
ctx[i] = canv[i].getContext('2d');
return(i);
}
function keyEvent(event) {
var i = 0;
while(isCanv[i]){
ctx[i].fillStyle="#00FFFF";
ctx[i].fillRect(0,0,800,800);
i++;
}
}
and the html looks like this
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>redicated</title>
</head>
<body style="background:#333333;" onkeydown="keyEvent(event)">
<div id="game"></div>
<script src="game.js"></script>
</body>
</html>
This works for the first canvas, but any subsequent addition breaks it all. Does anyone know how I could fix this, or of a better way of doing it?
Edit:
I figured it out. I need to recreate the context every time there is an addition. now my code looks like
function createCtx(){
var i = 0;
while(isCanv[i]){
i++;
}
inhtml[i] = '<canvas id="canv'+i+'" width="'+800+'px" height="'+800+'px" style="display:block;background:#ffffff+;"></canvas>';
isCanv[i] = true;
if(i>upperBound){
upperBound = i;
}
var tohtml = '';
for(var j = 0; j<= upperBound; j++){
if(isCanv[j]){
tohtml+=inhtml[j];
}
}
document.getElementById('game').innerHTML=tohtml;
for(var j = 0; j<= upperBound; j++){
if(isCanv[j]){
canv[j] = document.getElementById('canv'+j);
ctx[j] = canv[j].getContext('2d');
}
}
return(i);
}
1 answers
solution1
0
The for loop:
for(var j = 0; j<= upperBound; j++){
if(isCanv[i]){
tohtml+=inhtml[j];
}
is only ran once since when it is first executed j == upperBound. To fix this try removing
if(i>upperBound){
upperBound = i;
}
and whats the point of upperBound anyways it will always be equivalent to i so why not just use that.
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